The aim of the CircleP project is to develop an innovative, environmentally friendly and economically advantageous phosphorus-recovery technology suitable for small and medium wastewater treatment plants (WWTPs). The project focuses on developing new coagulants using the Baltic region’s untapped subsurface resources, including clays, their modification products, and promising calcium/iron-oxide composite materials (including srebrodolskite). After wastewater treatment, the phosphorus-saturated composite materials can be used in agriculture as alternative fertilisers with liming properties. To ensure the technology’s effectiveness, studies were carried out on the action of the coagulants in reducing phosphorus levels in wastewater, the efficiency of phosphorus recovery, and their sustainable use in agriculture. In addition, a technology-transfer strategy was developed. Young researchers and students from the University of Latvia’s Faculties of Geography and Earth Sciences, Chemistry and Biology, as well as from the Institute of Materials Mechanics and the RTU Department of Water Engineering and Technology, were involved in the project, thereby promoting interdisciplinarity and the development of young scientists’ competences. The project results were published in several scientific articles in Scopus and/or WoS databases, presented at local and international conferences, and popularised among the wider public through popular-science magazines, social media and various public and educational events, such as Researchers’ Night and the University of Latvia study festival “L-Universs”.